At present, a radio communication system wherein communication is carried out through a radio communication path as represented by a system of WCDMA, CDMA2000 or the like is used popularly in the world. In such a radio communication system as just described, a radio base station (BS; Base Station) is provided in a service area such that a radio terminal carries out communication with a different communication apparatus (communication terminal) through the radio base station.
FIG. 18 shows a connection scheme of the P-MP (Point to Multipoint) type wherein a radio base station 101 connects to a plurality of radio terminals (MS; Mobile Stations) 102 in a cover area (cell) 100 thereof. In the IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 802.16 which is the standards of high-speed radio data communication, such a P-MP scheme as shown in FIG. 18 is prescribed as a form of communication. Further, in the IEEE 802.16 WG, principally two kinds of specifications including the 802.16d specifications (802.16-2004) for point-to-point communication applications and the 802.16e specifications (802.16e-2005) for mobile communication applications are prescribed.
In such a P-MP type connection scheme as shown in FIG. 18, since the service area is limited to the inside of the cell 100 of the radio base station 101 and the radio environment is not good on the boundary (cell edge) of the cell 100, high-speed communication is in most cases difficult.
In order to solve this problem, the IEEE 802.16 WG establishes a task group 802.16j for developing a specification of a relay system where a relay station (RS; Relay Station) carries out relay between a radio base station and a radio terminal, and the working of the task group is proceeding at present.
It is to be noted that matters relating to the IEEE 802.16 described above are disclosed, for example, in Non-Patent Documents 1 to 3 listed hereinbelow.
Further, a technique is disclosed in Patent Document 1 listed hereinbelow wherein, in a relay system through a relay station, a radio base station decides scheduling in communication between a relay station and a radio terminal, and the relay station receives scheduling information between the relay station and the radio terminal from the radio base station and executes communication control between the relay station and the radio terminal based on the scheduling information. At this time, since the scheduling process is executed in a concentrated manner by the radio base station, it is sufficient for the relay station to have an easy implementation.
In the technique disclosed in Patent Document 1, where the overall scheduling in communication between the relay station and the radio terminal is carried out by the radio base station, it becomes necessary for the relay station to relay a signal and data received from the radio terminal to the radio station without changing the contents of the signal and the data. This is because the information of the radio terminal received by the relay station is required by the radio base station in order that the radio base station carries out, in place of the relay station, scheduling between the relay station and the radio terminal.
Non-Patent Document 1: IEEE Std802.16-2004
Non-Patent Document 2: IEEE Std802.16e-2005
Non-Patent Document 3: 2006 Comprehensive Meeting of The Japan Society of Information and Communication Research B-5-140 “Effects of the multiple MAP (map) in the IEEE 802.16 relay system”
Patent Document 1: Japanese Patent Laid-Open No. 2006-74325